1. Field of the Invention
The invention relates to fiberoptic sensors whose operation is based on varying the ratio of output power in a fiberoptic directional coupler.
2. Description of the Prior Art
Sensors, such as accelerometers, microphones, hydrophones and magnetometers including both electro-mechanical devices and, more recently, fiberoptic devices are well known. Fiberoptic sensors offer advantages in D.C. sensitivity, dynamic range, and interference rejection.
Existing fiberoptic sensors have used such principles as light phase interference, polarization rotation by means of birefringence and microbending loss. Prior art fiberoptic sensors may generally be categorized as either amplitude or phase (interferometric) sensors.
In an amplitude sensor, a physical perturbation interacts with the fiber or some device attached to the fiber to directly modulate the intensity of the light in the fiber. Phase sensors, while offering increased sensitity over amplitude sensors, are more complex. A detailed survey of fiberoptic sensors has been described by Giallorenzi, et al in "Optical Fiber Sensor Technology", IEEE Journal of Quantum Electronics, Vol. QE18, No. 4, April 1982, pp 626-665. While progress in fiberoptic technology has been rapid, practical problems remain, for example, in noise sources, detection processing and packaging. The present invention adds another category of fiberoptic sensors to the art which may be called ratio sensors. The ratio of light energy in the output fibers changes in response to applied stress on the medium surrounding a fiberoptic directional coupler.